<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		
		<script>
			var x = null;//值为null,但类型为对象
			var x = undefined;//值为undefined，类型也是undefined
			var x;//值为undefined，类型也是undefined
			x = undefined;//值为undefined，类型也是undefined
			//undefined 和 null 的区别
			console.log(typeof null);
			console.log(typeof undefined);
			console.log(null==undefined);
			console.log(null===undefined);
		</script>
	</body>
</html>